The invention relates to off-shore drilling and production structures, particularly, but not exclusively for use in Arctic waters, where environmental conditions present severe conditions for oil or gas production.
The southern Arctic ocean, particularly in the ice-shear zone of the continental shelf, in the Beaufort Sea, is the subject of intense investigation in the search for oil and gas resources.
Since ice covers the general area for up to nine months of the year, ice islands, and other large ice masses, such as ice ridges contained within the seasonal pack ice provide formidable obstacles to fixed off short installations. Ice islands, while rare, usually exceed 100 feet in thickness and may cover several square miles in area. Thus, it will be appreciated that the potential impact of ice on any sub-sea structure has necessitated the design and development of structures adapted to withstand what could be considered normal ice impingement.
There are presently available many different structural arrangements that have been designed with this problem in mind. Examples of such structures are found in U.S. Pat. Nos. 3,793,840 and 3,754,403 issued to Texaco Inc. during 1974; 3,952,527 issued to E. R. Vinieratos et al, in April, 1976 and 4,037,424 to E. O. Anders in July of 1977. Such structures however have numerous practical disadvantages since they, in the main, do not have the structural integrity to withstand the attack of frequently occurring large ice ridges. Furthermore, ice islands, drawing up to one hundred and fifty feet of water would pose intenable loads on any structure in their path. Therefore, there exists a need for a structure that may be simply installed, and capable of withstanding normal ice impingement forces, and further adapted to be quickly and easily dismounted to avoid impact with for example, ice islands or for re-emplacement at a different location.